Nature of the Low Field Transition in the Mixed State of High Temperature Superconductors

Abstract

We have numerically studied the statics and dynamics of a model three-dimensional vortex lattice at low magnetic fields. For the statics we use a frustrated 3D XY model on a stacked triangular lattice. We model the dynamics as a coupled network of overdamped resistively-shunted Josephson junctions with Langevin noise. At low fields, there is a weakly first-order phase transition, at which the vortex lattice melts into a line liquid. Phase coherence parallel to the field persists until a sharp crossover, conceivably a phase transition, near $T_{\ell }>T_m$ which develops at the same temperature as an infinite vortex tangle. The calculated flux flow resistivity in various geometries near $T=T_{\ell }$ closely resembles experiment. The local density of field induced vortices increases sharply near $T_{\ell }$, corresponding to the experimentally observed magnetization jump. We discuss the nature of a possible transition or crossover at $T_{\ell }$(B) which is distinct from flux lattice melting.

Updated references. 46 pages including low quality 25 eps figures. Contact [email protected] or visit http://www.physics.ohio-state.edu:80/~ryu/ for better figures and additional movie files from simulations. To be published in Physical Review B1 01Jun98

References in corpus (1)

• 3D XY and lowest Landau level fluctuations in deoxygenated YBCO thin films

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